1. Field of the Invention
The present invention relates to a disk device, such as a magnetic disk device or an optical magnetic disk device, for writing information (data) at an arbitrary position on a magnetic recording surface of a medium, represented by a disk such as a magnetic disk, with a magnetic head including a recording head element and a reproducing head element. More particularly, the present invention relates to a disk device having a function of controlling a magnetic space formed between a magnetic head and a medium on the disk when an amount of protrusion of a recording element or a reproducing element onto a magnetic recording surface of the medium is changed by heating the recording element or the reproducing element with a heater arranged close to the recording element or the reproducing element, according to an environment of the use of the disk device.
On the other hand, the present invention relates to a method of controlling the disk device for controlling the magnetic space formed between the magnetic head and the medium of the disk, by changing the amount of protrusion of the recording head element or the reproducing head element when the recording head element or the reproducing head element is heated by the heater element arranged close to the recording head element or the reproducing head element.
2. Description of the Related Art
In a disk device such as a magnetic disk device, data is written when information is recorded at arbitrary positions in a plurality of tracks concentrically formed on the disk in a region ranging from an outer circumferential portion of the disk to an inner circumferential portion of the disk with a recording head element of a magnetic head represented by a thin film magnetic head. Further, data is read out when information recorded at arbitrary positions in the plurality of tracks is reproduced with the reproducing head element of the magnetic head.
Concerning the magnetic recording system used at the time of recording data in the medium on the disk, the following two recording systems are provided. One is a longitudinal magnetic recording system, which has already been put into practical use, in which a direction of the magnetization signal agrees with an in-plane direction of the magnetic recording surface of the medium. The other is a perpendicular magnetic recording system in which a direction of the magnetization signal is vertical to the magnetic recording surface of the medium.
In a disk device in which either the longitudinal magnetic recording system or the perpendicular magnetic recording system is used, in general, in order to stably carry out the data writing operation and the data reading operation at an arbitrary position on the magnetic recording surface of the medium while the magnetic head is being moved under the condition that the magnetic head is floating above the magnetic recording surface of the medium, a predetermined magnetic space is provided between a head floating surface of the magnetic head and a magnetic recording surface of the medium. In this case, the terminology of “the head floating surface” denotes a surface of the magnetic head, which is held by a slider under the condition that the magnetic head is floating from the magnetic recording surface of the medium of the disk, opposed to the magnetic recording surface of the medium. Here, the head floating surface is referred to as an ABS (air bearing surface). Alternatively, the head floating surface is referred to as a surface facing to a medium.
Recently, there is a tendency that a storage capacity of a disk device such as a magnetic disk device has been remarkably increased. The increase in the storage capacity described above is mainly accomplished by an increase in the recording density on a magnetic recording surface of a medium. In order to increase the recording density as described above, two methods are provided. One is a method in which a core width of the magnetic head is reduced so as to increase the track density in the radial direction of the medium. The other is a method in which information is recorded relatively densely in the circumferential direction of the medium so as to increase the recording density in the bit direction.
Further, according to the environment of the use of the disk device, in order to further increase the storage capacity, it is necessary that S/N ratio (a ratio of signal to noise) in a regenerative signal reproduced by the reproducing head element is increased to as high as possible by decreasing an amount of floating of the magnetic head.
Therefore, it is conventional to use a disk device on which a magnetic head is mounted, which has a heater heating function including a heater element arranged close to a reproducing head element (or a recording head element). In the disk device having the above-mentioned configuration, the control of the magnetic head can be carried out as follows. In order to increase the S/N ratio of a regenerative signal of a reproducing head element according to the environment of the use of the disk device, a portion close to the reproducing head element is heated by the heater element so that an amount of protrusion of the reproducing element onto the magnetic recording surface can be intentionally increased and a magnetic space between the reproducing head element and the medium can be relatively decreased.
In general, in a disk device such as a magnetic disk device, in order to maintain a state in which a magnetic head is floating above a medium surface (a magnetic recording surface) of a medium, the magnetic head is mounted on a slider arranged at a forward end portion of a head supporting portion.
In a conventional magnetic disk device, when a heater element is arranged close to a reproducing head element in a magnetic head, the magnetic head having a heater heating function is formed. Usually, in order to protect the recording head element, the reproducing element and the heater element, the entire magnetic head is usually covered with a non-magnetic insulating layer made of alumina. In this case, when a portion close to the reproducing head element is heated by the heater element, alumina is expanded and a head floating surface (ABS) of the slider of the magnetic head is protruded out toward a medium surface. Therefore, an amount of protrusion of the reproducing head element in the magnetic head onto the medium surface is increased. Therefore, the amount of protrusion of the reproducing head element is controlled so that a magnetic space between the magnetic head and the medium can be relatively reduced. As a result, it becomes possible to increase the S/N ratio of the regenerative signal of the reproducing head element.
However, in the conventional disk device, when the reproducing head element is intentionally protruded, a magnetic space related to a head disk interface (HDI) between the magnetic head and the medium is decreased. Therefore, the magnetic head and the medium surface of the medium are likely to be contacted with each other by HDI. Owing to the contact of the magnetic head with the medium surface of the medium, a modulation is generated in the regenerative signal of the reproducing head element, and an output waveform of the regenerative signal fluctuates. Consequently, a problem may occur in that data can not be normally read out. Further, another problem may occur in that the reproducing head is physically damaged and the magnetic characteristic is deteriorated.
In this connection, Patent Document #1 (Japanese Unexamined Patent Publication (Kokai) No. 2000-251430) and Patent Document #2 (Japanese Unexamined Patent Publication (Kokai) No. 9-231502) are presented as technical documents of the prior art related to the conventional disk device described above. Patent Document #1 (JPP'430) discloses a magnetic disk device in which a collision of the magnetic head with the disk can be detected under a practically used environmental condition so that a fluctuation of the flying height (the flying amount) of the magnetic head can be estimated and so that a degree of danger of the head crash can be also estimated. The head collision detecting method in the magnetic disk device of Patent Document #1 is a method in which a gap (a magnetic space) related to HDI between the magnetic head and the disk is observed by a change in the output of a servo signal. In other words, this method is not a method in which a fluctuation caused by the modulation of the output waveform generated by the contact of the magnetic head with the disk is directly detected. The head collision detecting method disclosed in Patent Document #1 described above is disadvantageous in the following point. Even in the case in which an output of the regenerative signal of the magnetic head fluctuates, which is not based on a change in the floating amount of the magnetic head, it may be recognized that this output fluctuation is generated by a change in the floating amount of the magnetic head.
Patent Document #2 (JPP'502) discloses a method of inspecting a magnetic disk medium, in which a peak value of the spike-shaped waveform outputted from the detection means can be accurately detected; and a position of contact between the reproducing head element in the magnetic head and the magnetic disk medium can be accurately specified not only in the track direction but also in the circumferential direction so as to grasp a result of detection of the contact two-dimensionally. The above-mentioned method is a method in which a contact between the reproducing head and the magnetic disk medium is detected by utilizing thermal asperity (TA) of the reproducing head element. In this case, thermal asperity (TA) is a spike-shaped noise of the regenerative signal generated when the reproducing head element is instantaneously heated. In other words, the above-mentioned method is not a method in which a change in the output waveform caused by the modulation, which is generated by the contact between the magnetic head and the disk, is directly detected. Thermal asperity is a phenomenon in which, when the reproducing head such as a magneto-resistance effect element comes into contact with the medium, the temperature is raised and a change in the resistance of the reproducing head caused at this time affects the regenerative signal. Accordingly, the phenomenon of thermal asperity is not generated unless the reproducing head element itself directly collides with the medium. In other words, the above-mentioned method disclosed in Patent Document #2 is disadvantageous in the following point. In the case in which any portion other than the slider and the reproducing head element of the magnetic head comes into contact with the medium, it is impossible to accurately detect a contact between the magnetic head and the medium.
Therefore, both Patent Documents #1 and #2 have the following disadvantages. In the case in which the magnetic head and the medium are contacted with each other by HDI, the same problems as those of the disk device on which the conventional magnetic head having a heater heating function is mounted, may be caused.